Listeria monocytogenes vaccine vector

Listeria monocytogenes (LM) has been proposed as vaccine vector in various cancers and infectious diseases since LM induces a strong immune response. In this study, we developed a novel and safe LM-based vaccine vector platform, by engineering a triple attenuated mutant (Lm3Dx) (?actA, ?inlA, ?inlB) of the wild-type LM strain JF5203 (CC 1, phylogenetic lineage I). We demonstrated the strong attenuation of Lm3Dx while maintaining its capacity to selectively infect antigen presenting cells (APCs) in vitro. Furthermore, as proof of concept, we introduced the immunodominant Neospora caninum (Nc) surface antigen NcSAG1 into Lm3Dx. The NcSAG1 protein was expressed by Lm3Dx_SAG1 during cellular infection. To demonstrate safety and immunogenicity of Lm3Dx_SAG1 in vivo, we vaccinated BALB/C mice by intramuscular injection. Following vaccination, mice did not suffer any adverse effects and only sporadically shed bacteria at very low levels in the feces (<100 CFU/g). Additionally, only few bacteria or no bacteria were isolated from tissues 5 days after the 1st vaccination or 2 weeks after the second boost, respectively. Vaccination of mice prior and during pregnancy did not interfere with pregnancy outcome. Additionally, when inoculated during lactation, Lm3Dx_SAG1 did not cause any adverse effects in either dams or pups, although it was shed into the milk. Upon vaccination, mice developed a strong and Th1-biased immune response.